使用命名信号量在进程之间进行同步

Question

我正在尝试实现经典餐饮哲学家问题的改进形式。

假设桌上有5位哲学家。桌子上放着3把叉子和3把勺子。哲学家可以选择桌上的任何汤匙或叉子。哲学家需要叉子和勺子才能吃东西。

我正在用过程代表每个哲学家。我使用了两个名为semaphore的信号量：semf和semt分别代表叉子和勺子。

该过程没有同步化。证明这一点的一种简单方法是有两个哲学家，并提供一个汤匙和叉子。

代码如下：

#include <stdio.h>         
#include <stdlib.h>       
#include <sys/types.h>        
#include <errno.h>          
#include <semaphore.h>      
#include <fcntl.h>          

#define SEFORK "/eatingforksem"
#define SSPOON "/spoonsem"


int main()
{
    int i;                       
    pid_t pid;
    unsigned int n;             
    unsigned int fvalue;     
    unsigned int svalue;        

    printf ("How many Philosophers are sitting on the table?\n");
    printf ("Philosopher count: ");
    scanf ("%u", &n);

    printf ("Count of Eating Forks?\n");
    printf ("Eating Fork Count: ");
    scanf ("%u", &fvalue);

    printf ("Count of Eating Spoons?\n");
    printf ("Eating Spoon Count: ");
    scanf ("%u", &svalue);    


    sem_t *semf = sem_open(SEFORK, O_CREAT, 0644, fvalue); 
    sem_t *sems = sem_open(SSPOON, O_CREAT, 0644, svalue); 
    printf ("semaphores initialized.\n\n");


    for (i = 0; i < n; i++){
        pid = fork ();
        if (pid < 0) {
            sem_unlink (SEFORK);   
            sem_unlink (SSPOON);               
            sem_close(semf);  
            sem_close(sems);  
            printf ("Fork error.\n");
        }
        else if (pid == 0)
            break;                  /* child processes */
    }


    if (pid != 0){
        while (pid = waitpid (-1, NULL, 0)){
            if (errno == ECHILD)
                break;
        }

        sem_unlink (SEFORK);   
        sem_unlink (SSPOON);               
        sem_close(semf);  
        sem_close(sems);
        printf ("\nParent: All Philosphers have eaten.\n");

        exit (0);
    }
    else{

        sem_t *semf = sem_open(SEFORK, 0); 
        sem_t *sems = sem_open(SSPOON, 0); 
        printf(" Philosopher %d is thinking\n", i);
        sleep (3);
        printf(" Philosopher %d is hungry\n", i);
        sleep (3);                                           
        sem_wait (semf);
        printf(" Philosopher %d has picked a fork\n", i);
        sleep (3);           
        sem_wait (sems);
        printf(" Philosopher %d has picked a spoon and is eating\n", i);   
        sleep (3);
        sem_post (semf); 
        printf(" Philosopher %d has put down the fork\n", i);                    
        sem_post (sems);                           
        printf(" Philosopher %d has put down the spoon and finished eating\n", i); 
        sleep (3);          
        exit (0);
    }    


    return 0;
}

我正在使用带有标志-lpthread -lrt -pthread的gcc编译程序。